1. Field of the Invention
The invention relates to backup power supplies, and more particularly, to a system which detects and responds to changes in condition of a backup power supply.
2. Description of Related Art
The function of a traditional UPS (uninterruptible power supply) is to provide backup power to a system such as a PC (Personal Computer) in case of main power loss. This backup power enables the user of the system to close software applications and shut down the system to avoid data loss and file corruption which could occur if the system power is suddenly interrupted. However, the backup capacity of a UPS is normally limited to a few minutes, with the cost of the UPS being in proportion to the length of available backup time provided.
Problems arise when main power loss occurs while the system is unattended, or when, as in some applications, the data input devices which would normally allow the operator to perform graceful shutdown of the system are deliberately disabled, for safety or other reasons, upon the loss of main power. In these situations, performance of graceful shutdown is precluded, with a disruptive shutdown occurring at the expiration of backup power life if main power is not restored in time, thus inviting conditions for system file corruption and attendant complications. Such complications can result in significant problems--e.g., in situations where the PC is used to control a manufacturing process such as semiconductor etching or chemical vapor deposition (CVD), significant economic losses and time delays can be incurred.
Since the UPS cannot guarantee that backup power will last until main power, which can be main AC or DC power, is restored, there arises the need for a system which will automatically shut down operations in a graceful, nondisruptive manner. It would be desirable for a system to be sensitive to the current operations status of the system and to implement system shutdown only after ascertaining that it is safe to do so.